This invention relates to an improved apparatus for the scrubbing of a gas stream to remove entrained solid particles and other solid and condensable gaseous contaminants such as mist, or noxious gaseous compounds, and sulphur dioxide.
Industrial or commercial facilities often generate hot waste gas streams which are discharged to the atmosphere. These streams are generally ladened with entrained solids, mist, or gaseous contaminants such as sulphur dioxide, which must be removed prior to discharge into the atmosphere in order to reduce or prevent air pollution or to recover valuable entrained components. In recent years, more stringent air pollution regulations have been enacted in many communities, which have necessitated the provision of more efficient and effective facilities and apparatus for treating waste gases to remove entrained and contained contaminants and prevent or substantially reduce air pollution.
Generally, there have been two basic types of methods of extracting solid particles from gas streams, the dry process and the wet process. The dry process typically contemplates the use of electric precipitators or some type of filter or screening means, such as passing the gas through a dust bag. In many instances, the installation of conventional dry process equipment such as bag filters, is usually not warranted due to the cost of such facilities. Another dry process includes the use of cyclonic type separators. Dry processes are usually satisfactory if the entrained solid particles are relatively large, but these processes are not very successful when the entrained solid products are small, particularly when the solids are in submicron range. Electric precipitators are successful in extracting small particles, but these precipitators are usually prohibitively expensive when large gas volumes are involved.
Separators or scrubbers using a wet process are usually more effective in extracting solid particles of small dimension. Known wet scrubbers include means for passing gas through apparatus which include areas in which the gas is contacted by liquids. Water is the usual scrubbing liquid. This apparatus provides an intimate mixture of the scrubbing liquid and the gas to be treated. The apparatus is designed so that as the gas flows through the apparatus, it separates the liquid into extremely small liquid particles which contact the small solid particles entrained in the gas. Thereafter, the physical mixture of gas and entrained particles of scrubbing liquid containing the trapped solid particles and materials dissolved from the gas by the liquid is passed to an apparatus that separates the liquid particles from the gas. This apparatus may be, for example, a conventional moisture eliminator.
Conventional wet scrubbing apparatus is usually built with a specific combination of dimensions that are designed for a particular optimum rate of gas flow within a narrow range of flow rates. In order to secure maximum efficiency, each such scrubber must be designed and constructed for a specific flow rate. Any change in the flow rate or other perimeter of the scrubbing system, such as changes in gas or liquid pressures, size, weight and distribution of entrained particles, results in the apparatus functioning at less than its maximum designed effectiveness and efficiency. The construction of gas scrubbers has heretofore required specially designed apparatus having specifically dimensioned components and such scrubbers do not operate efficiently when the gas flow is below or exceeds the limited range for which the scrubber is designed. The prior art scrubbers generally fail to adequately compensate for variations in gas flow rate, such as is encountered in periodic cyclic or batch type processes which generate or discharge gas streams at varying or intermittent flow rates.
Various scrubbing apparatus have been designed which include vertically adjustable plugs which vary the throat of an adjustable angular venturi passage and thereby adjust the gas flow and pressure drop through the scrubber. Such scrubbers are shown in U.S. Pat. No. 3,544,086, U.S. Pat. No. 3,601,374, U.S. Pat. No. 3,690,044, U.S. Pat. No. 3,767,174, U.S. Pat. No. 3,199,267, U.S. Pat. No. 3,854,908, U.S. Pat. No. 3,844,744, and U.S. Pat. No. 3,976,454. All of these patents relate to generally similar scrubber designs in which a centrally located plug can be moved vertically to change the throat dimensions of an outer annular venturi passage by making the venturi passage adjustable, however, these scrubber designs do not provide the highly efficient particle remover capabilities of a fixed-throat venturi passage.